Last updated: 2026-09-01 · 5 min read

What Should a Dimensional Inspection Report Include — and How Do You Read One?

A dimensional inspection report is the document that tells you whether the mold builder made what the drawing asked for. It lists every critical dimension on the part, the nominal value from the drawing, the tolerance band, and the actual measured value from the CMM or optical comparator — side by side, in a format that lets you accept or reject each feature without ambiguity.

Process parameter — A controllable variable in the injection molding process: melt temperature, injection speed, holding pressure, cooling time, mold temperature. Each parameter affects part quality — deviations cause defects. Parameters are set during T1 and locked for production. See also related guide.

Key Facts

  • A complete report includes the part number, revision level, measurement date, CMM serial number, probe tip diameter, temperature at measurement, and the operator’s name.
  • Every dimension on the drawing must appear on the report — not just the ones the mold builder chose to measure. Missing dimensions mean the report is incomplete.
  • The report must use the same GD&T callouts as the drawing: if the drawing specifies a true-position tolerance at MMC, the report must state the measured position at the same material condition.

    • Process parameter — A controllable variable in the injection molding process: melt temperature, injection speed, holding pressure, cooling time, mold temperature. Each parameter affects part quality — deviations cause defects. Parameters are set during T1 and locked for production. The related guide covers adjacent topics.

    What a Proper Dimensional Report Looks Like

    The standard format is a table with columns for item number, feature description, nominal value, tolerance, upper limit, lower limit, measured value, and pass/fail status. Some reports add a deviation column that shows the measured value minus the nominal — this makes it easy to see which dimensions are drifting toward the tolerance boundary.

    Column Purpose What to Check
    Item No. references the balloon number on the drawing every ballooned dimension has a matching row
    Feature description of the measured feature clear enough to identify without the drawing
    Nominal value from the drawing matches the latest revision of the 2D drawing
    Tolerance ± or unilateral same format as drawing (not converted)
    Measured actual CMM or comparator reading reported to one more decimal than the tolerance
    Pass/Fail in or out of tolerance flagged items must have a disposition note

    What Makes a Report Unusable

  • Dimensions missing from the report — if the drawing has 45 ballooned dimensions and the report shows 30, the remaining 15 are unverified and the part cannot be accepted.
  • Wrong drawing revision — the report references revision A but the current drawing is revision C; the nominal values and tolerances may have changed.
  • No measurement conditions listed — temperature affects every dimension; a part measured at 28 °C in a workshop reads differently from one measured at 20 °C in a CMM lab.
    The report must state the ambient temperature.
  • Measured values rounded to the tolerance boundary — if the tolerance is ±0.05 mm and the measured value is reported as “within tolerance” without a number, the reader cannot assess how close the dimension is to the limit or whether it is trending out.
  • GD&T callouts reduced to plus/minus — a true-position tolerance at MMC is not the same as a ± tolerance on X and Y coordinates.
    If the report converts GD&T to coordinate tolerances, the measurement does not verify what the drawing specified.

    • One pattern that signals an incomplete report: the mold builder measures only the easy-to-dimensions with calipers and skips the internal features that require a CMM probe or an optical comparator.
    The report looks complete on paper because every dimension has a value — but the measurement method is not stated, and the caliper readings on features that need CMM precision are unreliable.

    How to Use the Report at T1 Acceptance

    At T1, the dimensional report is the primary acceptance document. The process has three steps: verify the report format against the drawing, review each out-of-tolerance dimension for disposition, and archive the raw CMM data file alongside the PDF report.

    For any dimension that fails — measured value outside the tolerance band — the mold builder must propose a disposition: re-cut the cavity, adjust the process window, or request a drawing change. The customer reviews each disposition and signs off or rejects it. A T1 report with 5 failed dimensions and signed dispositions for each is a better acceptance document than a report with zero failures and no traceability to how the measurements were taken.

    The raw CMM data file matters. A PDF report is a snapshot — the raw data file contains the full point cloud, the probe compensation, and the datum reference frame. If a dimension is disputed later (during production or at the customer’s incoming inspection), the raw file is the only way to re-analyze the measurement without re-measuring the part.

    Frequently Asked Questions

    How many parts should the T1 dimensional report cover?

    At minimum, one part from each cavity in a multi-cavity mold. For a 4-cavity tool, the report should include measurements from all 4 cavities — not just cavity 1. If only one cavity is measured, the remaining cavities are unverified.

    What is the difference between a first-article inspection and a T1 dimensional report?

    A T1 report is measured on parts from the first mold trial, often with the process window still being established. A first-article inspection (FAI per AS9102 or similar) is measured on parts from the validated production process. T1 proves the mold geometry; FAI proves the mold plus process together.

    Should the mold builder measure the cavity or the part?

    Both serve different purposes. Measuring the cavity verifies that the steel was cut correctly. Measuring the part verifies that the mold produces parts to drawing. The T1 report should measure the part — the cavity measurement is the mold builder’s internal quality check and should be available on request.

    Key Takeaways

    1. A dimensional report that omits any ballooned dimension from the drawing is incomplete — do not accept the tool until every dimension is measured and reported.
    2. The measured value must be a number, not “within tolerance” — the customer needs the number to assess trend, not just pass/fail.
    3. The raw CMM data file is part of the deliverable; a PDF without the raw file is not fully traceable.

    The dimensional report is the last document before the customer signs the T1 acceptance. If it does not answer every question the drawing raises, the acceptance is based on trust rather than evidence — and trust is not a measurement method.

    Sources
    Mitutoyo — measurement instruments
    Zeiss — industrial metrology
    ASTM — standards for measurement

    Sources: Plastics Technology · Plastics Technology Online · Society of Plastics Engineers (SPE) · ThomasNet